Dendritic cells are antigen-presenting cells that are found in all tissues and organs, including the blood. Specifically, dendritic cells present antigens for T lymphocytes, i.e., they process and present antigens, and stimulate responses from naive and memory T cells. In addition to their role in antigen presentation, dendritic cells directly communicate with non-lymph tissue and survey non-lymph for an injury signal (e.g., ischemia, infection, or inflammation) or tumor growth. Once signaled, dendritic cells initiate the immune response by releasing IL-1 which triggers lymphocytes and monocytes.
Dendritic cells can play either a positive or negative role in various immunologically related situations. For example, dendritic cells are thought to be involved in transplant rejection and autoimmune diseases, and it may be desirable to block their function in such situations. On the other hand, various immunodeficiencies, e.g., towards tumors, may result from deficient dendritic cells. In addition, there is evidence that HIV can infect certain populations of dendritic cells.
It is desirable to obtain substantially pure populations of dendritic cells, e.g., in order to exploit the important role of dendritic cells in various immunotherapies. Dendritic cell isolation is particularly difficult, however, because it is believed that they are very low in frequency in blood and other tissues, and because there is no reported surface marker expressed by fresh and cultured dendritic cells which distinguishes it from monocytes. Conventional methods for isolation which enrich subpopulations of cell mixtures include, e.g., density gradient separation, fluorescence activated cell sorting, immunological cell separation techniques such as panning, complement lysis, resetting, magnetic cell separation techniques, and nylon wool separation. Different patterns of expression of cell surface antigens have been used in some cases to identify different cell types. Certain disadvantages of many of these reported methods are that they can be time-consuming, labor-intensive, costly, require large amounts of reagent, can result in low specificity, low sensitivity, contaminated mixtures, poor and/or inaccurate separation, loss of desired cells, or can change the properties, functions, or viability of the desired cells. Thus, prior methods generally are inefficient, time-consuming, expensive and do not optimize for pure populations.